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Positive feedback between MAP kinase and Mos during Xenopus oocyte maturation
W T Matten1, T D Copeland, N G Ahn
1ABL-Basic Research Program, NCI-Frederick Cancer Research and Development Center, Frederick, Maryland 21702, USA.
Abstract:
Mos is a serine-threonine protein kinase and a key regulator of meiosis. One function of Xenopus Mos is to activate mitogen-activated protein kinase (MAPK) through direct phosphorylation and activation of MAPK kinase (MAPKK). All three members of this signal cascade can individually induce hormone-independent reentry of oocytes into meiosis I. However, their inducing efficiency is reduced in the absence of protein synthesis. Here we show that de novo Mos synthesis is required for induction of meiosis I by active MAPKK or Mos-MAPK coinjection. In addition, MAPK efficiently phosphorylates Mos at Ser-3 in vitro. These results suggest that a positive feedback loop exists between MAPK and Mos during oocyte maturation. De novo synthesis of Mos, and other proteins, is required for progression from meiosis I to the metaphase arrest at meiosis II; therefore, one function of MAPK during normal Xenopus oocyte maturation might be to stimulate the synthesis or accumulation of Mos that is required for the completion of meiosis.
Insights
New protein synthesis, including Mos, is essential for Xenopus oocyte maturation. MAPK signaling appears to stimulate Mos synthesis, creating a positive feedback loop for meiotic progression.
Area of Science:
- Cell Biology
- Molecular Biology
- Developmental Biology
Background:
- Mos is a serine-threonine protein kinase regulating meiosis.
- Mos activates mitogen-activated protein kinase (MAPK) via MAPK kinase (MAPKK).
- Protein synthesis is necessary for efficient meiotic induction by this cascade.
Purpose of the Study:
- To investigate the role of de novo Mos synthesis in Xenopus oocyte maturation.
- To elucidate the relationship between MAPK and Mos during oocyte maturation.
Main Methods:
- Coinjection of active MAPKK or Mos-MAPK into Xenopus oocytes.
- In vitro phosphorylation assays of Mos by MAPK.
Main Results:
- De novo Mos synthesis is required for meiosis I induction by MAPKK or Mos-MAPK.
- MAPK phosphorylates Mos at Ser-3 in vitro, suggesting a positive feedback mechanism.
- MAPK may stimulate Mos synthesis for progression through meiosis.
Conclusions:
- A positive feedback loop between MAPK and Mos is crucial for oocyte maturation.
- MAPK-mediated stimulation of Mos synthesis is vital for completing meiosis I and arresting at meiosis II.